Origin and Chemical Nature
Epinephrine is a naturally occurring biogenic catecholamine. Under physiological conditions, it is the primary hormone of the adrenal medulla, where it is continuously synthesized and stored by specialized chromaffin cells.
For pharmaceutical and medical use, the drug is obtained either via directed chemical synthesis or by extraction from the adrenal tissues of livestock.
Pharmacodynamics and Receptor Profile
The main pharmacological feature of epinephrine is its non-selectivity. Unlike norepinephrine (norepinephrine), which has virtually no activity at $\beta_2$-adrenergic receptors, epinephrine is a potent agonist at both $\alpha$- and $\beta$-adrenergic receptors.
It is the action on vascular $\beta_2$-adrenergic receptors—stimulation of which leads to vasodilation—that dictates its specific hemodynamic profile. Following the administration of epinephrine, a sharp rise in blood pressure (BP) is inevitably followed by a subsequent drop. This secondary hypotensive phase is entirely absent with norepinephrine.
Metabolic Effects and Clinical Application
In addition to its pronounced pressor effects on the cardiovascular system, epinephrine actively alters metabolic processes, primarily carbohydrate metabolism. The drug rapidly increases systemic blood glucose levels.
In clinical practice, this metabolic effect is utilized for emergency care. Epinephrine is used to treat hypoglycemic coma—a life-threatening condition caused by a critical drop in blood sugar (e.g., due to an overdose of insulin or other hypoglycemic agents).
Pharmaceutical Features: Epinephrine Salts
In pharmacies and hospitals, the drug is available in two salt forms: hydrochloride (Adrenalini hydrochloridum) and hydrotartrate (bitartrate).
From a pharmacodynamic and therapeutic standpoint, these forms are entirely identical. However, clinicians must account for a key dosing nuance: the molecular weight of the hydrotartrate salt is significantly greater than that of the hydrochloride. Because of this difference, achieving a comparable clinical effect requires a higher absolute dose of epinephrine hydrotartrate compared to the hydrochloride.
Formulations and Administration Guidelines
The standard formulations and routes of administration include:
- Ampoule Solution: 0.1% solution in 1 mL. Administered subcutaneously (SC), intramuscularly (IM), and intravenously (IV).
- Ophthalmic Forms: 0.5% eye drops and a 2% solution in 10 mL bottles. Administered topically, 1–2 drops into the conjunctival sac.
- Injection Dosing: Single doses generally range from 0.0003 to 0.00075 g. Prior to intravenous administration, the drug must be diluted in 15–20 mL of normal saline (0.9% NaCl).
- Dose Limits: The maximum single dose (MSD) for subcutaneous administration is strictly limited to 0.001 g. The maximum daily dose (MDD) for subcutaneous administration must not exceed 0.005 g.